(1) Field of the Invention
This invention relates to producing oil wells and more particularly to a time measurement and counting means.
(2) Description of the Prior Art
Pump off condition exists in an oil well when the amount of liquid in the bottom of the well is insufficient to properly load the reciprocating pump for each stroke. It is a well recognized problem and many solutions have been sought for it. E.g., SMITH, U.S. Pat. No. 2,550,093 discloses a system wherein the well fluids are pumped against a spring loaded check valve which is above ground.
COTTRELL, U.S. Pat. No. 3,274,940, discloses a system where the fluid from the pump is pumped into a chamber which has a float operated switch therein.
URMANN et al., U.S. Pat. No. 2,690,713, discloses a system where the level of the liquid in the well is determined which is used to initiate a signal to control the pump operation.
AGNEW et al., U.S. Pat. No. 3,075,466, discloses a system where the variation of the currents drawn by the pump motor is used to control.
DOUGLAS, U.S. Pat. No. 3,854,846, discloses a system where pressure pulses are used in a control system. This patent also discloses the specific electrical circuit necessary for permanently shutting down a pumping system until it is manually restarted, if several restarts fail to cause the flow high enough to actuate a reset signal.
Before filing this application the inventors caused a search in the U.S. Patent and Trademark Office to be made which disclosed the following patents:
Tilley et al.--U.S. Pat. No. 3,269,320 PA2 Skinner, II et al.--U.S. Pat. No. 3,665,960 PA2 Mills--U.S. Pat. No. 3,851,995 PA2 Watson--U.S. Pat. No. 3,965,983
TILLEY et al. discloses equipment wherein sonic means is used to determine the pounding which occurs at pump off. After a predetermined cumulative duration of the pounding the well is shut off.
WATSON discloses a system for using the timing of sound waves to determine the level of the liquid within the well.
The other patents discovered on the search do not seem to be as pertinent as those specifically discussed above.